This invention relates to a steer-by-wire handwheel actuator incorporating a mechanism for variable end-of-travel.
Current steer-by-wire steering systems are incapable of providing tactile indication of steering end-of-travel to the driver if the kinematic relationship between the steering wheel angle command from the driver and the position of the front road wheels is adjusted by electronic controls. This kinematic relationship is commonly referred to as the overall steering ratio. Traditional, mechanically linked steering systems have a mechanically constrained steering ratio that is determined by steering gear ratio, steering arm length and the physical orientation of the steering gear and the front road wheel assemblies in the vehicle. Current steer-by-wire handwheel actuators allow for only a fixed angular travel of the steering wheel. This invention improves the steer-by-wire system by allowing the control electronics to adjust the overall steering ratio in response to vehicle dynamics. Control software also provides an adjustable end of steering travel indication to the driver when the front road wheels have reached their maximum angular travel. This provides an indication of front road wheel end-of-travel as well as road force feedback to the driver.
It is therefore an objective of the present invention to provide a steer-by-wire handwheel actuator in a vehicle. The handwheel actuator comprises a controller operative to accept as input thereto data from the steer-by-wire system and generate therefrom control signals; a driver input shaft; a gear train connected to the driver input shaft; a variable stop motor responsive to the control signals from the controller and variably geared to the gear train; a feedback motor responsive to the control signals from the controller and geared to one of the driver input shaft and the gear train; and a stop mechanism attached to a housing and coupled to one of the feedback motor and the gear train.
It is also an object of the present invention to provide a method of varying the gear ratio of a handwheel actuator of a steer-by-wire steering system comprising measuring the position of the driver input shaft; measuring the speed of the vehicle; and calculating the desired position of the end-of-travel of the driver input shaft. The method further comprises measuring the position of the stop mechanism; and providing a first control signal to the variable stop motor for controlling the input of the variable stop motor to the planetary gear train.
It is still further an object of the present invention to provide a method of providing tactile response to a driver of a steer-by-wire handwheel actuator. The method comprises measuring the road forces acting upon the steer-by-wire system; measuring the position of the driver input shaft; measuring speed of the vehicle; and calculating the desired feedback torque of the driver input shaft. The method further comprises measuring the torque of the driver input shaft; and providing a second control signal to the feedback motor for controlling the feedback torque of the feedback motor to the driver input shaft or the carrier.